This invention relates to controlled-release fertilizers. In particular, it relates to controlled-release fertilizers that contain urea-formaldehyde and supply, inter alia, nitrogen to plants.
It is advantageous to supply to plants the necessary nutrients, such as nitrogen, phosphorous and potassium at a controlled rate commensurate with the utilization of the nutrients by the plant. In order to fulfill this objective a number of controlled-release fertilizer delivery systems have been developed.
One system for controlled-release fertilizers utilizes urea-formaldehyde to bind the fertilizer material, thus retarding release of plant fertilizer materials into the soil. Such a system is described for example in U.S. Pat. No. 4,348,218 (Bond). In this system urea-formaldehyde acts merely as a binder and does not substantially supply nitrogen to the plant. The nitrogen sources in this composition are usually ammonium salts or inorganic nitrates. The urea-formaldehyde resin used in this system has a urea to formaldehyde molar ratio of about 0.5 to 1. An example of such urea-formaldehyde is RESIMINE UF 71 sold by Monsanto Company.
U.S. Pat. No. 4,063,919 (Grano, Jr.) discloses a fertilizer rod made of poly(vinyl alcohol), a plasticizer and a fertilizer (plant nutrient) which includes partly water-soluble urea formaldehyde.
U.S. Pat. No. 4,014,675 (Osburn) discloses a fertilizer stick composed of a hydroxy propyl cellouse thermoplastic material containing 10-80 weight percent of fertilizer material, such as ureaform. See Column 1, lines 59-63. The fertilizer can also include potash. Column 3, line 17.
The shaped fertilizer products for controlled release of fertilizers using poly(vinyl alcohol) as a binder and partly water-soluble urea-formaldehyde as the source of fertilizer nitrogen have been commercially sold in the United States for years. One such product is made as follows:
(a) about 44 weight percent of poly(vinyl alcohol); PA1 (b) about 13-30 weight percent of urea-formaldehyde condensate having a mole ratio of urea to formaldehyde of about 1.25 to 1.4, such as BFC'S NITROFORM; PA1 (c) about 25 to 42 weight percent of a mixture of inorganic materials supplying phosphorous and potassium; and PA1 (d) about 1 weight percent of an inert plasticizer such as CARBOWAX 400 manufactured by Union Carbide Corporation.
The above ingredients are mixed together in a fluidizing mixer and the resulting mixture is fed into a heated extruder having the following temperature distribution:
______________________________________ Zone One 220-240.degree. F. Zone Two 240-260.degree. F. Zone Three 260-280.degree. F. Zone Four 280-310.degree. F. Gate 310-340.degree. F. Die 340-380.degree. F. ______________________________________
Only a small portion of the nitrogen contained in the resulting fertilizer product is available for sustained-release during the growing period of a plant (a several month period). The amount of available sustained-release nitrogen was measured by standard method of analysis--Method 2.079 described in Methods of Analysis of the Association of Official Analytical Chemists (13th ed. 1980) (hereinafter AOAC), except that nitrogen quantity was determined in the hot water extract rather than in residue. The tests described on the products made in accordance with the procedures described above show that only about 5 weight percent of the total nitrogen is available for sustained release during the growing period of a plant.
Since the amount of sustained-release nitrogen in the urea-formaldehyde prior to making the fertilizer products was about 30 weight percent, some of the sustained-release nitrogen becomes unavailable during processing. Accordingly, the activity index (hereinafter AI) (which is another indication of the sustained release characteristic of nitrogen in urea-formaldehyde fertilizer products) is severely reduced during processing. The definition of the activity index is described in Method 2.079 of AOAC.
Similarly, in the processes disclosed in the Grano, Jr. and Osburn patents the AI of the urea-formaldehyde condensate is significantly reduced during the manufacturing of the fertilizer products. Therefore, significantly less of the controlled release fraction of the urea formaldehyde condensate is available for plant nutrition. The amount of the controlled release fraction is of such enormous importance to effective utilization of the fertilizer products that laws have been promulgated to prevent sales of product having controlled function below a certain minimum level as measured by the Activity Index. The manufacturing of shaped products in accordance with prior art methods reduces AI of the urea formaldehyde condensate below the level acceptable in at least some European countries. Accordingly, it is not possible to sell fertilizer products utilizing urea formaldehyde condensate as a nitrogen source in combination with other plant nutrients in these countries. Even in countries which do not have requirements for the minimum activity index of fertilizer products, the loss of the slow release fraction as measured by the AI results in inferior product performance.
The problem of unavailability of nitrogen has been recognized by the art. For example, in U.S. Pat. No. 4,052,190 (Berliner), the patentee states that urea-formaldehyde is an expensive form of nitrogen in part because considerable amounts thereof are fixed and, therefore, never become available for plant growth. See Column 1, lines 19-28 of the Berliner patent.
Despite its high cost, it is desirable to use urea-formaldehyde condensate as the source of nitrogen for several reasons. First, the utilization efficiency of nitrogen by plants is much higher than those provided by other nitrogen sources. Second, it is impossible to overdose and hence "burn" a plant by using urea-formaldehyde condensate but not when using other types of nitrogen sources. Third, fewer salts are introduced into the soil around the plant when using urea-formaldehyde condensate. Fourth, urea-formaldehyde condensate includes three fractions of nitrogen, the first of which becomes available in a matter of days, the second in a matter of months and the third in a matter of years. Thus, sustained release is built into the product.
There is, therefore, a need for a complete fertilizer product containing a urea-formaldehyde condensate as a source of nitrogen which contains amounts of sustained-release nitrogen that approximate those in urea-formaldehyde condensate feed stock and a process for making such fertilizer products.
Thus, one object of the present invention is to provide a fertilizer product that contains a proportionally increased amount of sustained-release nitrogen when compared with prior art products made from the same ingredients.
Another object of the present invention is to provide a process for making a urea-formaldehyde containing fertilizer product that does not significantly diminish the amounts of sustained-release nitrogen available in the urea-formaldehyde condensate.
A further object of the present invention is to maintain the activity index (AI) of the urea-formaldehyde condensate in the fertilizer product at the level approximating that of the urea-formaldehyde condensate feedstock.
Still another object of the present invention is to provide a process that does not significantly diminish the urea-formaldehyde activity index (AI) during processing into a fertilizer product.
Other objects of the present invention will become apparent to those skilled in the art upon studying this specification.